With the introduction of the Public Switched Telephone Network, the following data networks were developed: Local Area Networks (LANs), which typically use Ethernet technology within a single location; Metropolitan Area Networks (MANs), which typically use optical fiber technology for communication within a larger area such as a city; and Wide Area Networks (WANs), where communication is spread over an even greater area, such as a country. Now by using radio technologies, wireless equivalents of these fixed-wire networks have been developed. These wireless equivalents are especially useful with the transmission of broadband services. Such a wireless equivalent is typically called a Wireless Local Area Network (WLAN).
WLANs use electromagnetic airwaves (radio and infrared) to communicate information from point to point without the need for a physical connection. The data being transmitted is superimposed or modulated on the radio wave (also known as a radio carrier) and the data will be extracted at the receiving end. The transmitter/receiver (transceiver) device, called an access point (AP), connects to the wired network from a fixed location and receives, buffers, and transmits data between the wired network and the WLAN. A single access point can support a small group of users. Access points can extend the range of independent WLANs by acting as a repeater, and can potentially double the distance between wireless systems or computers.
The last few years have witnessed an explosive growth of IEEE 802.11 WLANs. From all indications, this growth is expected to continue at exponential rates. From university campuses, business offices, homes, to airport lounges, coffee shops and other public/private locations, untethered Internet access is prevalent, thanks to the widely deployed WLANs.
One of the most logical progressions for WLANs is to have a structured organization of access points, and the communication between these access points can be flexibly implemented via either wired or wireless mediums. This will result in better coverage of a service area and improved coordination among access points. The majority of today's WLANs, nevertheless, are based on isolated deployment of “hot spot” topology, where each access point serves as a dumb gateway between the mobile devices associated with it and the rest of the Internet. Only a limited number of multi-AP topology has been deployed, using a hodgepodge of technologies without the desired system performance.
Meanwhile, the market demand for a networking technology covering an area with a collection of communicating nodes, commonly called mesh network, is beginning to take shape. Mesh networks are multi-hop systems in which communicating nodes assist each other in transmitting packets through the network. Instead of using the current “hub and spoke” model of wireless communications, where a base station connected to an Internet Service Provider, via satellite or a landline, connects to customers through a rooftop antenna (which can be overburdened at times), the mesh network automatically creates a wireless loop for any devices that are close to one another. In such a system, data can hop from one part of the network to another part of the network. However, a concern with mesh network arrangements is the creation of unwanted traffic on the wireless network and bandwidth management. It would be desirable to provide a mesh network system that overcomes these deficiencies.
Further, various governmental agencies around the world have initiated projects for metropolitan area coverage using WLAN technologies and many institutions are exploring similar network deployments. Service providers anticipate that this technology will offer a significant opportunity for a profitable service model.
Not surprisingly, the IEEE 802.11 standard-making body recognizes the market need for metropolitan area coverage by using WLAN technologies and thus has formed a task group, called TGs, for investigating mesh networks. TGs expects some of the benefits of such mesh networks to include easier deployment, more efficient spectral reuse, better Quality of Service (QoS) support, and improved system management. To date, TGs has identified a number of usage models (including residential, office, campus, and temporary public work areas), categorized functionalities and carved out the scope of the standardization work. Currently TGs is soliciting technical proposals for this standard-making process.
Presently, the IEEE 802.11 standard carves up its operating spectrum into a number of channels, however, these channels are not used simultaneously in a system for increased bandwidth. At startup, access points scan the operating spectrum and use the first available channel for communication. Even when the interference of the communication channel becomes high, access points will reduce the modulating scheme (lower data rate) instead of switching to another channel.
Accordingly, a novel technology is needed to meet the challenges outlined above. The present invention provides an architectural framework for mesh networks, which incorporates a novel algorithm for network discovery, organization, channel assignment and reassignment. Over this framework, other enhancements can be incorporated while interoperability with higher layer protocols is maintained.
Further objects and advantages of the present invention will become apparent from a consideration of the drawings and ensuing description thereof.